This invention relates generally to apparatus for developing latent images with particulate developer. More particularly, this invention relates to magnetic brush development apparatus for developing a latent image carried by a support which is passed through a development zone which is inclined at a predetermined angle to the horizontal.
In electrography, it is common to form an electrostatic image on an electrophotographic member such as a drum, web or sheet and to develop that image by applying developer particles thereto. The developed image is either transferred to a receiving member and fixed to such member or is fixed to the electrophotographic member itself.
The electrostatic image may be developed by means of a non-magnetic cascade system or by means of magnetic systems with either single component or two-component magnetic magnetic developer. In two-component development systems, the developer includes magnetic carrier particles and toner particles which are electrostatically attached to the carrier either by electrostatic charging or by triboelectric charging. In such systems, the magnetic carrier particles are held to a non-magnetic applicator surface in a bristle formation by a magnetic assembly located within the applicator. Either the magnet or the applicator rotates to brush the surface of a member carrying an electrostatic image. The electrostatic image is developed by the attraction between the toner and the charged image which overcomes the electrostatic attraction between the magnetic particles and the toner. In single-component development systems, the magnetic particle itself is attracted to the electrostatic image for development. If the magnetic particles are insulating, they are electrostatically charged so that they are attracted to the electrostatic to develop it. Alternatively, if the magnetic particles are relatively conductive, they are attracted to the electrostatic image by means of a charge induced by an electrical potential applied between the electrostatically charged surface and an electrically conductive applicator.
Some magnetic brush development apparatus include a sump which extends the length of the development zone and which contains the magnetic developer. The magnetic brush transports developer from the sump to the development zone and back to the sump. There is a tendency in such apparatus for toner to settle at the bottom of the sump causing loss of usable developer and requiring more frequent replenishment than should be necessary. In single-component magnetic developer apparatus, a magnetic brush applicator may be supplied with magnetic developer by means of a hopper which extends the length of the applicator. The rate at which developer is supplied to the applicator should equal the rate at which it is carried off by developed supports to avoid waste of developer. Otherwise, since developer is usually not recirculated in hopper-type apparatus, a waste container must be provided resulting in costly and inefficient use of developer. In hopper-fed apparatus, there is also a tendency for developer to cake up between the hopper outlet and developer applicator causing uneven application of developer to a support and consequent image defects. In both sump and hopper-fed development apparatus, developer is supplied across the length of the applicator and developer does not tend to move laterally along the applicator due to the influence of gravity since the applicator is generally horizontally oriented. However, electrographic reproduction systems may be used with a microfilm reader-printer which is inclined to the horizontal in order to provide for operator convenience in viewing and operation. In such apparatus, the development zone of electrographic printer is transversely inclined at a predetermined angle to the horizontal and development apparatus which used sumps or hoppers to supply developer would be inadequate due to the tendency of the developer to accumulate at the lower end of the development apparatus due to the influence of gravity.